Matt Sheahan brings us up to speed with the ACCWing wingsail that could well become automated in the future
The words ‘muscles’ and ‘sails’ are often included in the same sentence, such is the physical nature of our sport. But what I hadn’t expected to hear in a recent techie chat was talk of a sail that had its own muscle power. The conversation was about a new type of wingsail that could provide solutions to several of the issues that have held such configurations back so far.
Low drag, minimal mast compression and low loads are just three of the key advantages a wingsail offers over the conventional approach of a single skin sail and have been well known for some time. Plenty have tried to make the idea work, yet none have hit the big time.
When the America’s Cup world threw big bucks at wingsails for the 34th America’s Cup and wing-masted cats back in 2010, the technology and understanding around how to build, control and handle wingsails accelerated rapidly.
Today, the configuration remains the sail plan of choice aboard the F50s in SailGP and the development continues. The fleet now has three wing sizes and these high speed foiling cats can operate across an impressively wide range of conditions.
In light, single figure wind speeds they’re super efficient and help to deliver double figure speeds. At the top end of the scale, in, say, 20-plus knots of breeze, they’re held back not by the limits of their small rigs, but by the cavitation on the T-foil rudders as they approach the 50-knot mark.
It’s not just speed that has been whetting appetites in the design world. Sheet loads are relatively low, it’s easy to depower them, plus – as has been seen in the two multihull America’s Cup cycles – if you twist off the top section to the point that it now hangs out to leeward you can generate righting moment at the top of the rig as well, further increasing the power.
But wingails aren’t without their drawbacks when it comes to physically handling them. Not only are they large, unwieldy and potentially difficult to manage in a breeze, but the need to build them light means they’re fragile too. Lifting them in and out of the boat is tricky. And reefing? Forget it.
There are a few concepts that have used reefing and the physical handling as their starting points – the Omer wingsail, the Beneteau wingsail system and the IWS inflatable wing – and now there’s the ACCWing.
Developed by Hugues De Turckheim (who brought us the Tiga windsurfer) and Philippe Marcovich, the ACCWing is essentially a twin skinned sail that can be raised or lowered like several of the others. It’s fully battened and can be reefed. But the difference is that this wing can change its section shape using its own internal muscles operated by compressed air. Unlike flaps that create an abrupt change to the section shape, the ACCWing is a far smoother affair.
It achieves this with ‘muscles’ fitted at various positions up the sail on the inside of the wing. The muscles consist of a braided line around flexible hoses, one on each side of the wing. When the hose contracts on one side, it pulls the sail into shape creating a deeper camber. It’s ingenious stuff.
The fact there are muscles at different positions up the sail means the section shape can change with height allowing the twist to be controlled, developing a smooth transition from top to bottom.
When it comes to sheet loads, wingsails are often light thanks to the balancing effect of the sail ahead of the mast, much like the balance achieved on a spade rudder. With this in mind it’s easy to see why Marcovich says the sail can be easily automated.
In fact, on a 72m-long superyacht-styled vessel that’s about to go into build with a triple ACCWing system that has 16,000ft2 there are no mainsheets. Instead, the rotation of the masts change the angle of attack of the sail.
From here it’s easy to imagine how this system could be totally automated to respond to wind speed and direction both in section shape and include automated reefing too.
While you might turn your nose up at letting a computer and a bunch of servos take over a key part of the boat, there will surely be shipping companies that’ll sit up and take note. Since the clipper ships went out of fashion there’s never been any need for them to put muscles and sails in the same sentence. Until now.
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